The aggregation of dihydrogen phosphate ion has been studied by Raman
spectroscopy during serial dilution of highly concentrated (>5 M) solu
tions. Factor analysis has been used to recover monomer and aggregate
spectra from families of 600-2000 spectra obtained during dilution to
about 0.1 M. Spectra of the free aquated dihydrogen phosphate ion and
its dimer, trimer, and tetramer have been obtained. There is some evid
ence for the existence of longer chain aggregates. The serial dilution
procedure has been verified by dilution of 2.3 M glycine solution. On
ly spectra of monomer and dimer ions are recovered. For the well-under
stood glycine system, the band positions and intensities and the dimer
ization concentration-dependence are in agreement with previously repo
rted values.